x86/traps: address violation of MISRA C Rule 8.4

Rule 8.4 states: "A compatible declaration shall be visible when
an object or function with external linkage is defined".

The function do_general_protection is either used is asm code
or only within this unit, so there is no risk of this getting
out of sync with its definition, but the function must remain
extern.

Therefore, this function is deviated using a comment-based deviation.
No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/traps.c

@@ -1257,6 +1257,7 @@ void asmlinkage do_int3(struct cpu_user_regs *regs)
     pv_inject_hw_exception(X86_EXC_BP, X86_EVENT_NO_EC);
 }
 
+/* SAF-1-safe */
 void do_general_protection(struct cpu_user_regs *regs)
 {
 #ifdef CONFIG_PV